From 2c25fb2ede5bf3432d2019756cc2d588a4cb794f Mon Sep 17 00:00:00 2001
From: Damien Miller <djm@mindrot.org>
Date: Mon, 26 Mar 2012 23:10:27 +1100
Subject: [PATCH] refactor agent client code

removed fatal()
buffer_ => sshbuf_
changed lookup of identies to return a fully-deserialised list of keys
removed AuthenticationConnection abstration; all operations now use plain socket
---
 ssh/authfd.c      | 894 ++++++++++++++++++++++++----------------------
 ssh/authfd.h      |  57 ++-
 ssh/clientloop.c  |  18 +-
 ssh/err.c         |   4 +
 ssh/err.h         |   2 +
 ssh/ssh-add.c     | 141 +++++---
 ssh/ssh.c         |   8 +-
 ssh/sshconnect1.c |  68 ++--
 ssh/sshconnect2.c |  57 +--
 9 files changed, 671 insertions(+), 578 deletions(-)

diff --git a/ssh/authfd.c b/ssh/authfd.c
index fb4001f..350f2b5 100644
--- a/ssh/authfd.c
+++ b/ssh/authfd.c
@@ -43,6 +43,7 @@
 #include <openssl/evp.h>
 
 #include <openssl/crypto.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <stdlib.h>
 #include <signal.h>
@@ -52,7 +53,7 @@
 #include "xmalloc.h"
 #include "ssh.h"
 #include "rsa.h"
-#include "buffer.h"
+#include "sshbuf.h"
 #include "key.h"
 #include "authfd.h"
 #include "cipher.h"
@@ -63,110 +64,106 @@
 #include "misc.h"
 #include "err.h"
 
-static int agent_present = 0;
-
-/* helper */
-int	decode_reply(int type);
+#define MAX_AGENT_IDENTITIES	2048		/* Max keys in agent reply */
+#define MAX_AGENT_REPLY_LEN	(256 * 1024) 	/* Max bytes in agent reply */
 
 /* macro to check for "agent failure" message */
 #define agent_failed(x) \
-    ((x == SSH_AGENT_FAILURE) || (x == SSH_COM_AGENT2_FAILURE) || \
+    ((x == SSH_AGENT_FAILURE) || \
+    (x == SSH_COM_AGENT2_FAILURE) || \
     (x == SSH2_AGENT_FAILURE))
 
-int
-ssh_agent_present(void)
+/* Convert success/failure response from agent to a err.h status */
+static int
+decode_reply(u_char type)
 {
-	int authfd;
-
-	if (agent_present)
-		return 1;
-	if ((authfd = ssh_get_authentication_socket()) == -1)
+	if (agent_failed(type))
+		return SSH_ERR_AGENT_FAILURE;
+	else if (type == SSH_AGENT_SUCCESS)
 		return 0;
-	else {
-		ssh_close_authentication_socket(authfd);
-		return 1;
-	}
+	else
+		return SSH_ERR_INVALID_FORMAT;
 }
 
 /* Returns the number of the authentication fd, or -1 if there is none. */
-
 int
-ssh_get_authentication_socket(void)
+ssh_get_authentication_socket(int *fdp)
 {
 	const char *authsocket;
-	int sock;
+	int sock, oerrno;
 	struct sockaddr_un sunaddr;
 
+	if (fdp != NULL)
+		*fdp = -1;
+
 	authsocket = getenv(SSH_AUTHSOCKET_ENV_NAME);
 	if (!authsocket)
-		return -1;
+		return SSH_ERR_AGENT_NOT_PRESENT;
 
 	bzero(&sunaddr, sizeof(sunaddr));
 	sunaddr.sun_family = AF_UNIX;
 	strlcpy(sunaddr.sun_path, authsocket, sizeof(sunaddr.sun_path));
 
-	sock = socket(AF_UNIX, SOCK_STREAM, 0);
-	if (sock < 0)
-		return -1;
+	if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) < 0)
+		return SSH_ERR_SYSTEM_ERROR;
 
 	/* close on exec */
-	if (fcntl(sock, F_SETFD, FD_CLOEXEC) == -1) {
+	if (fcntl(sock, F_SETFD, FD_CLOEXEC) == -1 ||
+	    connect(sock, (struct sockaddr *)&sunaddr, sizeof(sunaddr)) < 0) {
+		oerrno = errno;
 		close(sock);
-		return -1;
+		errno = oerrno;
+		return SSH_ERR_SYSTEM_ERROR;
 	}
-	if (connect(sock, (struct sockaddr *)&sunaddr, sizeof sunaddr) < 0) {
+	if (fdp != NULL)
+		*fdp = sock;
+	else
 		close(sock);
-		return -1;
-	}
-	agent_present = 1;
-	return sock;
+	return 0;
 }
 
+/* Communicate with agent: send request and read reply */
 static int
-ssh_request_reply(AuthenticationConnection *auth, Buffer *request, Buffer *reply)
+ssh_request_reply(int sock, struct sshbuf *request, struct sshbuf *reply)
 {
-	u_int l, len;
+	int r;
+	size_t l, len;
 	char buf[1024];
 
 	/* Get the length of the message, and format it in the buffer. */
-	len = buffer_len(request);
+	len = sshbuf_len(request);
 	put_u32(buf, len);
 
 	/* Send the length and then the packet to the agent. */
-	if (atomicio(vwrite, auth->fd, buf, 4) != 4 ||
-	    atomicio(vwrite, auth->fd, buffer_ptr(request),
-	    buffer_len(request)) != buffer_len(request)) {
-		error("Error writing to authentication socket.");
-		return 0;
-	}
+	if (atomicio(vwrite, sock, buf, 4) != 4 ||
+	    atomicio(vwrite, sock, sshbuf_ptr(request),
+	    sshbuf_len(request)) != sshbuf_len(request))
+		return SSH_ERR_AGENT_COMMUNICATION;
 	/*
 	 * Wait for response from the agent.  First read the length of the
 	 * response packet.
 	 */
-	if (atomicio(read, auth->fd, buf, 4) != 4) {
-	    error("Error reading response length from authentication socket.");
-	    return 0;
-	}
+	if (atomicio(read, sock, buf, 4) != 4)
+	    return SSH_ERR_AGENT_COMMUNICATION;
 
 	/* Extract the length, and check it for sanity. */
 	len = get_u32(buf);
-	if (len > 256 * 1024)
-		fatal("Authentication response too long: %u", len);
+	if (len > MAX_AGENT_REPLY_LEN)
+		return SSH_ERR_INVALID_FORMAT;
 
 	/* Read the rest of the response in to the buffer. */
-	buffer_clear(reply);
+	sshbuf_reset(reply);
 	while (len > 0) {
 		l = len;
 		if (l > sizeof(buf))
 			l = sizeof(buf);
-		if (atomicio(read, auth->fd, buf, l) != l) {
-			error("Error reading response from authentication socket.");
-			return 0;
-		}
-		buffer_append(reply, buf, l);
+		if (atomicio(read, sock, buf, l) != l)
+			return SSH_ERR_AGENT_COMMUNICATION;
+		if ((r = sshbuf_put(reply, buf, l)) != 0)
+			return r;
 		len -= l;
 	}
-	return 1;
+	return 0;
 }
 
 /*
@@ -174,7 +171,6 @@ ssh_request_reply(AuthenticationConnection *auth, Buffer *request, Buffer *reply
  * obtained).  The argument must have been returned by
  * ssh_get_authentication_socket().
  */
-
 void
 ssh_close_authentication_socket(int sock)
 {
@@ -182,80 +178,105 @@ ssh_close_authentication_socket(int sock)
 		close(sock);
 }
 
-/*
- * Opens and connects a private socket for communication with the
- * authentication agent.  Returns the file descriptor (which must be
- * shut down and closed by the caller when no longer needed).
- * Returns NULL if an error occurred and the connection could not be
- * opened.
- */
-
-AuthenticationConnection *
-ssh_get_authentication_connection(void)
-{
-	AuthenticationConnection *auth;
-	int sock;
-
-	sock = ssh_get_authentication_socket();
-
-	/*
-	 * Fail if we couldn't obtain a connection.  This happens if we
-	 * exited due to a timeout.
-	 */
-	if (sock < 0)
-		return NULL;
-
-	auth = xmalloc(sizeof(*auth));
-	auth->fd = sock;
-	buffer_init(&auth->identities);
-	auth->howmany = 0;
-
-	return auth;
-}
-
-/*
- * Closes the connection to the authentication agent and frees any associated
- * memory.
- */
-
-void
-ssh_close_authentication_connection(AuthenticationConnection *auth)
-{
-	buffer_free(&auth->identities);
-	close(auth->fd);
-	xfree(auth);
-}
-
 /* Lock/unlock agent */
 int
-ssh_lock_agent(AuthenticationConnection *auth, int lock, const char *password)
+ssh_lock_agent(int sock, int lock, const char *password)
 {
-	int type;
-	Buffer msg;
+	int r;
+	u_char type = lock ? SSH_AGENTC_LOCK : SSH_AGENTC_UNLOCK;
+	struct sshbuf *msg;
 
-	buffer_init(&msg);
-	buffer_put_char(&msg, lock ? SSH_AGENTC_LOCK : SSH_AGENTC_UNLOCK);
-	buffer_put_cstring(&msg, password);
+	if ((msg = sshbuf_new()) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+	if ((r = sshbuf_put_u8(msg, type)) != 0 ||
+	    (r = sshbuf_put_cstring(msg, password)) != 0)
+		goto out;
+	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
+		goto out;
+	if ((r = sshbuf_get_u8(msg, &type)) != 0)
+		goto out;
+	r = decode_reply(type);
+ out:
+	sshbuf_free(msg);
+	return r;
+}
 
-	if (ssh_request_reply(auth, &msg, &msg) == 0) {
-		buffer_free(&msg);
-		return 0;
+static int
+deserialise_identity1(struct sshbuf *ids, struct sshkey **keyp, char **commentp)
+{
+	struct sshkey *key;
+	int r, keybits;
+	u_int32_t bits;
+	char *comment = NULL;
+
+	if ((key = sshkey_new(KEY_RSA1)) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+	if ((r = sshbuf_get_u32(ids, &bits)) != 0 ||
+	    (r = sshbuf_get_bignum1(ids, key->rsa->e)) != 0 ||
+	    (r = sshbuf_get_bignum1(ids, key->rsa->n)) != 0 ||
+	    (r = sshbuf_get_cstring(ids, &comment, NULL)) != 0)
+		goto out;
+	keybits = BN_num_bits(key->rsa->n);
+	/* XXX previously we just warned here. I think we should be strict */
+	if (keybits < 0 || bits != (u_int)keybits) {
+		r = SSH_ERR_KEY_BITS_MISMATCH;
+		goto out;
 	}
-	type = buffer_get_char(&msg);
-	buffer_free(&msg);
-	return decode_reply(type);
+	if (keyp != NULL) {
+		*keyp = key;
+		key = NULL;
+	}
+	if (commentp != NULL) {
+		*commentp = comment;
+		comment = NULL;
+	}
+	r = 0;
+ out:
+	sshkey_free(key);
+	free(comment);
+	return r;
+}
+
+static int
+deserialise_identity2(struct sshbuf *ids, struct sshkey **keyp, char **commentp)
+{
+	int r;
+	char *comment = NULL;
+	u_char *blob = NULL;
+	size_t blen;
+
+	if ((r = sshbuf_get_string(ids, &blob, &blen)) != 0 ||
+	    (r = sshbuf_get_cstring(ids, &comment, NULL)) != 0)
+		goto out;
+	if ((r = sshkey_from_blob(blob, blen, keyp)) != 0)
+		goto out;
+	if (commentp != NULL) {
+		*commentp = comment;
+		comment = NULL;
+	}
+	r = 0;
+ out:
+	if (blob != NULL) {
+		bzero(blob, blen);
+		free(blob);
+	}
+	free(comment);
+	return r;
 }
 
 /*
- * Returns the first authentication identity held by the agent.
+ * Fetch list of identities held by the agent.
  */
-
 int
-ssh_get_num_identities(AuthenticationConnection *auth, int version)
+ssh_fetch_identitylist(int sock, int version, struct ssh_identitylist **idlp)
 {
-	int type, code1 = 0, code2 = 0;
-	Buffer request;
+	u_char type, code1 = 0, code2 = 0;
+	u_int32_t num, i;
+	struct sshbuf *msg;
+	struct ssh_identitylist *idl = NULL;
+	int r;
 
+	/* Determine request and expected response types */
 	switch (version) {
 	case 1:
 		code1 = SSH_AGENTC_REQUEST_RSA_IDENTITIES;
@@ -266,291 +287,314 @@ ssh_get_num_identities(AuthenticationConnection *auth, int version)
 		code2 = SSH2_AGENT_IDENTITIES_ANSWER;
 		break;
 	default:
-		return 0;
+		return SSH_ERR_INVALID_ARGUMENT;
 	}
 
 	/*
 	 * Send a message to the agent requesting for a list of the
 	 * identities it can represent.
 	 */
-	buffer_init(&request);
-	buffer_put_char(&request, code1);
+	if ((msg = sshbuf_new()) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+	if ((r = sshbuf_put_u8(msg, code1)) != 0)
+		goto out;
 
-	buffer_clear(&auth->identities);
-	if (ssh_request_reply(auth, &request, &auth->identities) == 0) {
-		buffer_free(&request);
-		return 0;
-	}
-	buffer_free(&request);
+	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
+		goto out;
 
 	/* Get message type, and verify that we got a proper answer. */
-	type = buffer_get_char(&auth->identities);
+	if ((r = sshbuf_get_u8(msg, &type)) != 0)
+		goto out;
 	if (agent_failed(type)) {
-		return 0;
+		r = SSH_ERR_AGENT_FAILURE;
+		goto out;
 	} else if (type != code2) {
-		fatal("Bad authentication reply message type: %d", type);
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
 	}
 
 	/* Get the number of entries in the response and check it for sanity. */
-	auth->howmany = buffer_get_int(&auth->identities);
-	if ((u_int)auth->howmany > 1024)
-		fatal("Too many identities in authentication reply: %d",
-		    auth->howmany);
-
-	return auth->howmany;
-}
-
-struct sshkey *
-ssh_get_first_identity(AuthenticationConnection *auth, char **comment, int version)
-{
-	/* get number of identities and return the first entry (if any). */
-	if (ssh_get_num_identities(auth, version) > 0)
-		return ssh_get_next_identity(auth, comment, version);
-	return NULL;
-}
-
-struct sshkey *
-ssh_get_next_identity(AuthenticationConnection *auth, char **comment, int version)
-{
-	int keybits, ret;
-	u_int bits;
-	u_char *blob;
-	u_int blen;
-	struct sshkey *key = NULL;
-
-	/* Return failure if no more entries. */
-	if (auth->howmany <= 0)
-		return NULL;
-
-	/*
-	 * Get the next entry from the packet.  These will abort with a fatal
-	 * error if the packet is too short or contains corrupt data.
-	 */
-	switch (version) {
-	case 1:
-		if ((key = sshkey_new(KEY_RSA1)) == NULL)
-			fatal("%s: sshkey_new failed", __func__);
-		bits = buffer_get_int(&auth->identities);
-		buffer_get_bignum(&auth->identities, key->rsa->e);
-		buffer_get_bignum(&auth->identities, key->rsa->n);
-		*comment = buffer_get_string(&auth->identities, NULL);
-		keybits = BN_num_bits(key->rsa->n);
-		if (keybits < 0 || bits != (u_int)keybits)
-			logit("Warning: identity keysize mismatch: actual %d, announced %u",
-			    BN_num_bits(key->rsa->n), bits);
-		break;
-	case 2:
-		blob = buffer_get_string(&auth->identities, &blen);
-		*comment = buffer_get_string(&auth->identities, NULL);
-		if ((ret = sshkey_from_blob(blob, blen, &key)) != 0)
-			fatal("%s: sshkey_from_blob: %s",
-			    __func__, ssh_err(ret));
-		xfree(blob);
-		break;
-	default:
-		return NULL;
+	if ((r = sshbuf_get_u32(msg, &num)) != 0)
+		goto out;
+	if (num > MAX_AGENT_IDENTITIES) {
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
 	}
-	/* Decrement the number of remaining entries. */
-	auth->howmany--;
-	return key;
+	if (num == 0) {
+		r = SSH_ERR_AGENT_NO_IDENTITIES;
+		goto out;
+	}
+
+	/* Deserialise the response into a list of keys/comments */
+	if ((idl = calloc(1, sizeof(*idl))) == NULL ||
+	    (idl->keys = calloc(num, sizeof(*idl->keys))) == NULL ||
+	    (idl->comments = calloc(num, sizeof(*idl->comments))) == NULL) {
+		r = SSH_ERR_ALLOC_FAIL;
+		goto out;
+	}
+	for (i = 0; i < num; i++) {
+		switch (version) {
+		case 1:
+			if ((r = deserialise_identity1(msg,
+			    &(idl->keys[i]), &(idl->comments[i]))) != 0)
+				goto out;
+			break;
+		case 2:
+			if ((r = deserialise_identity2(msg,
+			    &(idl->keys[i]), &(idl->comments[i]))) != 0)
+				goto out;
+			break;
+		}
+	}
+	idl->nkeys = num;
+	*idlp = idl;
+	idl = NULL;
+	r = 0;
+ out:
+	sshbuf_free(msg);
+	if (idl != NULL)
+		ssh_free_identitylist(idl);
+	return r;
+}
+
+void
+ssh_free_identitylist(struct ssh_identitylist *idl)
+{
+	size_t i;
+
+	if (idl == NULL)
+		return;
+	for (i = 0; i < idl->nkeys; i++) {
+		if (idl->keys != NULL)
+			sshkey_free(idl->keys[i]);
+		if (idl->comments != NULL)
+			free(idl->comments[i]);
+	}
+	free(idl);
 }
 
 /*
- * Generates a random challenge, sends it to the agent, and waits for
- * response from the agent.  Returns true (non-zero) if the agent gave the
- * correct answer, zero otherwise.  Response type selects the style of
- * response desired, with 0 corresponding to protocol version 1.0 (no longer
- * supported) and 1 corresponding to protocol version 1.1.
+ * Sends a challenge (typically from a server via ssh(1)) to the agent,
+ * and waits for a response from the agent.
+ * Returns true (non-zero) if the agent gave the correct answer, zero
+ * otherwise.
  */
-
 int
-ssh_decrypt_challenge(AuthenticationConnection *auth,
-    struct sshkey* key, BIGNUM *challenge,
-    u_char session_id[16],
-    u_int response_type,
-    u_char response[16])
+ssh_decrypt_challenge(int sock, struct sshkey* key, BIGNUM *challenge,
+    u_char session_id[16], u_char response[16])
 {
-	Buffer buffer;
-	int success = 0;
-	int i;
-	int type;
+	struct sshbuf *msg;
+	int r;
+	u_char type;
 
 	if (key->type != KEY_RSA1)
-		return 0;
-	if (response_type == 0) {
-		logit("Compatibility with ssh protocol version 1.0 no longer supported.");
-		return 0;
-	}
-	buffer_init(&buffer);
-	buffer_put_char(&buffer, SSH_AGENTC_RSA_CHALLENGE);
-	buffer_put_int(&buffer, BN_num_bits(key->rsa->n));
-	buffer_put_bignum(&buffer, key->rsa->e);
-	buffer_put_bignum(&buffer, key->rsa->n);
-	buffer_put_bignum(&buffer, challenge);
-	buffer_append(&buffer, session_id, 16);
-	buffer_put_int(&buffer, response_type);
-
-	if (ssh_request_reply(auth, &buffer, &buffer) == 0) {
-		buffer_free(&buffer);
-		return 0;
-	}
-	type = buffer_get_char(&buffer);
-
+		return SSH_ERR_INVALID_ARGUMENT;
+	if ((msg = sshbuf_new()) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+	if ((r = sshbuf_put_u8(msg, SSH_AGENTC_RSA_CHALLENGE)) != 0 ||
+	    (r = sshbuf_put_u32(msg, BN_num_bits(key->rsa->n))) != 0 ||
+	    (r = sshbuf_put_bignum1(msg, key->rsa->e)) != 0 ||
+	    (r = sshbuf_put_bignum1(msg, key->rsa->n)) != 0 ||
+	    (r = sshbuf_put_bignum1(msg, challenge)) != 0 ||
+	    (r = sshbuf_put(msg, session_id, sizeof(session_id))) != 0 ||
+	    (r = sshbuf_put_u32(msg, 1)) != 0) /* Response type for proto 1.1 */
+		goto out;
+	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
+		goto out;
+	if ((r = sshbuf_get_u8(msg, &type)) != 0)
+		goto out;
 	if (agent_failed(type)) {
-		logit("Agent admitted failure to authenticate using the key.");
+		r = SSH_ERR_AGENT_FAILURE;
+		goto out;
 	} else if (type != SSH_AGENT_RSA_RESPONSE) {
-		fatal("Bad authentication response: %d", type);
-	} else {
-		success = 1;
-		/*
-		 * Get the response from the packet.  This will abort with a
-		 * fatal error if the packet is corrupt.
-		 */
-		for (i = 0; i < 16; i++)
-			response[i] = (u_char)buffer_get_char(&buffer);
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
 	}
-	buffer_free(&buffer);
-	return success;
+	if ((r = sshbuf_get(msg, response, sizeof(response))) != 0)
+		goto out;
+	r = 0;
+ out:
+	sshbuf_free(msg);
+	return r;
 }
 
 /* ask agent to sign data, returns err.h code on error, 0 on success */
 int
-ssh_agent_sign(AuthenticationConnection *auth,
-    struct sshkey *key,
+ssh_agent_sign(int sock, struct sshkey *key,
     u_char **sigp, u_int *lenp,
     u_char *data, u_int datalen, u_int compat)
 {
-	Buffer msg;
+	struct sshbuf *msg;
 	u_char *blob;
-	u_int blen;
-	int type, flags = 0;
-	int r, ret = SSH_ERR_AGENT_FAILURE;
-
-	if ((r = sshkey_to_blob(key, &blob, &blen)) != 0) {
-		error("%s: sshkey_to_blob: %s", __func__, ssh_err(r));
-		return SSH_ERR_INVALID_ARGUMENT;
-	}
+	u_int blen, flags = 0;
+	u_char type;
+	size_t len;
+	int r;
 
 	if (compat & SSH_BUG_SIGBLOB)
-		flags = SSH_AGENT_OLD_SIGNATURE;
-
-	buffer_init(&msg);
-	buffer_put_char(&msg, SSH2_AGENTC_SIGN_REQUEST);
-	buffer_put_string(&msg, blob, blen);
-	buffer_put_string(&msg, data, datalen);
-	buffer_put_int(&msg, flags);
-	xfree(blob);
-
-	if (ssh_request_reply(auth, &msg, &msg) == 0) {
-		buffer_free(&msg);
-		return SSH_ERR_AGENT_COMMUNICATION;
-	}
-	type = buffer_get_char(&msg);
+		flags |= SSH_AGENT_OLD_SIGNATURE;
+	if ((msg = sshbuf_new()) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+	if ((r = sshkey_to_blob(key, &blob, &blen)) != 0)
+		goto out;
+	if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 ||
+	    (r = sshbuf_put_string(msg, blob, blen)) != 0 ||
+	    (r = sshbuf_put_string(msg, data, datalen)) != 0 ||
+	    (r = sshbuf_put_u32(msg, flags)) != 0)
+		goto out;
+	if ((r = ssh_request_reply(sock, msg, msg) != 0))
+		goto out;
+	if ((r = sshbuf_get_u8(msg, &type)) != 0)
+		goto out;
 	if (agent_failed(type)) {
-		logit("Agent admitted failure to sign using the key.");
+		r = SSH_ERR_AGENT_FAILURE;
+		goto out;
 	} else if (type != SSH2_AGENT_SIGN_RESPONSE) {
-		fatal("Bad authentication response: %d", type);
-	} else {
-		ret = 0;
-		*sigp = buffer_get_string(&msg, lenp);
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
 	}
-	buffer_free(&msg);
-	return ret;
+	if ((r = sshbuf_get_string(msg, sigp, &len)) != 0)
+		goto out;
+	*lenp = len;
+	r = 0;
+ out:
+	if (blob != NULL) {
+		bzero(blob, blen);
+		free(blob);
+	}
+	sshbuf_free(msg);
+	return r;
 }
 
 /* Encode key for a message to the agent. */
 
-static void
-ssh_encode_identity_rsa1(Buffer *b, RSA *key, const char *comment)
+static int
+ssh_encode_identity_rsa1(struct sshbuf *b, RSA *key, const char *comment)
 {
-	buffer_put_int(b, BN_num_bits(key->n));
-	buffer_put_bignum(b, key->n);
-	buffer_put_bignum(b, key->e);
-	buffer_put_bignum(b, key->d);
+	int r;
+
 	/* To keep within the protocol: p < q for ssh. in SSL p > q */
-	buffer_put_bignum(b, key->iqmp);	/* ssh key->u */
-	buffer_put_bignum(b, key->q);	/* ssh key->p, SSL key->q */
-	buffer_put_bignum(b, key->p);	/* ssh key->q, SSL key->p */
-	buffer_put_cstring(b, comment);
+	if ((r = sshbuf_put_u32(b, BN_num_bits(key->n))) != 0 ||
+	    (r = sshbuf_put_bignum1(b, key->n)) != 0 ||
+	    (r = sshbuf_put_bignum1(b, key->e)) != 0 ||
+	    (r = sshbuf_put_bignum1(b, key->d)) != 0 ||
+	    (r = sshbuf_put_bignum1(b, key->iqmp)) != 0 ||
+	    (r = sshbuf_put_bignum1(b, key->q)) != 0 ||
+	    (r = sshbuf_put_bignum1(b, key->p)) != 0 ||
+	    (r = sshbuf_put_cstring(b, comment)) != 0)
+		return r;
+	return 0;
 }
 
-static void
-ssh_encode_identity_ssh2(Buffer *b, struct sshkey *key, const char *comment)
+static int
+ssh_encode_identity_ssh2(struct sshbuf *b, struct sshkey *key,
+    const char *comment)
 {
-	buffer_put_cstring(b, sshkey_ssh_name(key));
+	int r;
+
+	if ((r = sshbuf_put_cstring(b, sshkey_ssh_name(key))) != 0)
+		return r;
 	switch (key->type) {
 	case KEY_RSA:
-		buffer_put_bignum2(b, key->rsa->n);
-		buffer_put_bignum2(b, key->rsa->e);
-		buffer_put_bignum2(b, key->rsa->d);
-		buffer_put_bignum2(b, key->rsa->iqmp);
-		buffer_put_bignum2(b, key->rsa->p);
-		buffer_put_bignum2(b, key->rsa->q);
+		if ((r = sshbuf_put_bignum2(b, key->rsa->n)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->rsa->e)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->rsa->d)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->rsa->iqmp)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->rsa->p)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->rsa->q)) != 0)
+			return r;
 		break;
 	case KEY_RSA_CERT_V00:
 	case KEY_RSA_CERT:
-		if (key->cert == NULL || buffer_len(key->cert->certblob) == 0)
-			fatal("%s: no cert/certblob", __func__);
-		buffer_put_string(b, buffer_ptr(key->cert->certblob),
-		    buffer_len(key->cert->certblob));
-		buffer_put_bignum2(b, key->rsa->d);
-		buffer_put_bignum2(b, key->rsa->iqmp);
-		buffer_put_bignum2(b, key->rsa->p);
-		buffer_put_bignum2(b, key->rsa->q);
+		if (key->cert == NULL || sshbuf_len(key->cert->certblob) == 0)
+			return SSH_ERR_INVALID_ARGUMENT;
+		if ((r = sshbuf_put_stringb(b, key->cert->certblob)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->rsa->d)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->rsa->iqmp)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->rsa->p)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->rsa->q)) != 0)
+			return r;
 		break;
 	case KEY_DSA:
-		buffer_put_bignum2(b, key->dsa->p);
-		buffer_put_bignum2(b, key->dsa->q);
-		buffer_put_bignum2(b, key->dsa->g);
-		buffer_put_bignum2(b, key->dsa->pub_key);
-		buffer_put_bignum2(b, key->dsa->priv_key);
+		if ((r = sshbuf_put_bignum2(b, key->dsa->p)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->dsa->q)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->dsa->g)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->dsa->pub_key)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->dsa->priv_key)) != 0)
+			return r;
 		break;
 	case KEY_DSA_CERT_V00:
 	case KEY_DSA_CERT:
-		if (key->cert == NULL || buffer_len(key->cert->certblob) == 0)
-			fatal("%s: no cert/certblob", __func__);
-		buffer_put_string(b, buffer_ptr(key->cert->certblob),
-		    buffer_len(key->cert->certblob));
-		buffer_put_bignum2(b, key->dsa->priv_key);
+		if (key->cert == NULL || sshbuf_len(key->cert->certblob) == 0)
+			return SSH_ERR_INVALID_ARGUMENT;
+		if ((r = sshbuf_put_stringb(b, key->cert->certblob)) != 0 ||
+		    (r = sshbuf_put_bignum2(b, key->dsa->priv_key)) != 0)
+			return r;
 		break;
 	case KEY_ECDSA:
-		buffer_put_cstring(b, sshkey_curve_nid_to_name(key->ecdsa_nid));
-		buffer_put_ecpoint(b, EC_KEY_get0_group(key->ecdsa),
-		    EC_KEY_get0_public_key(key->ecdsa));
-		buffer_put_bignum2(b, EC_KEY_get0_private_key(key->ecdsa));
+		if ((r = sshbuf_put_cstring(b,
+		    sshkey_curve_nid_to_name(key->ecdsa_nid))) != 0 ||
+		    (r = sshbuf_put_eckey(b, key->ecdsa)) != 0 ||
+		    (r = sshbuf_put_bignum2(b,
+		    EC_KEY_get0_private_key(key->ecdsa))) != 0)
+			return r;
 		break;
 	case KEY_ECDSA_CERT:
-		if (key->cert == NULL || buffer_len(key->cert->certblob) == 0)
-			fatal("%s: no cert/certblob", __func__);
-		buffer_put_string(b, buffer_ptr(key->cert->certblob),
-		    buffer_len(key->cert->certblob));
-		buffer_put_bignum2(b, EC_KEY_get0_private_key(key->ecdsa));
+		if (key->cert == NULL || sshbuf_len(key->cert->certblob) == 0)
+			return SSH_ERR_INVALID_ARGUMENT;
+		if ((r = sshbuf_put_stringb(b, key->cert->certblob)) != 0 ||
+		    (r = sshbuf_put_bignum2(b,
+		    EC_KEY_get0_private_key(key->ecdsa))) != 0)
+			return r;
 		break;
 	}
-	buffer_put_cstring(b, comment);
+	if ((r = sshbuf_put_cstring(b, comment)) != 0)
+		return r;
+	return 0;
+}
+
+static int
+encode_constraints(struct sshbuf *m, u_int life, u_int confirm)
+{
+	int r;
+
+	if (life != 0) {
+		if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_LIFETIME)) != 0 ||
+		    (r = sshbuf_put_u32(m, life)) != 0)
+			goto out;
+	}
+	if (confirm != 0) {
+		if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_CONFIRM)) != 0)
+			goto out;
+	}
+	r = 0;
+ out:
+	return r;
 }
 
 /*
- * Adds an identity to the authentication server.  This call is not meant to
- * be used by normal applications.
+ * Adds an identity to the authentication server.
+ * This call is intended only for use by ssh-add(1) and like applications.
  */
-
 int
-ssh_add_identity_constrained(AuthenticationConnection *auth, struct sshkey *key,
-    const char *comment, u_int life, u_int confirm)
+ssh_add_identity_constrained(int sock, struct sshkey *key, const char *comment,
+    u_int life, u_int confirm)
 {
-	Buffer msg;
-	int type, constrained = (life || confirm);
+	struct sshbuf *msg;
+	int r, constrained = (life || confirm);
+	u_char type;
 
-	buffer_init(&msg);
+	if ((msg = sshbuf_new()) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
 
 	switch (key->type) {
 	case KEY_RSA1:
 		type = constrained ?
 		    SSH_AGENTC_ADD_RSA_ID_CONSTRAINED :
 		    SSH_AGENTC_ADD_RSA_IDENTITY;
-		buffer_put_char(&msg, type);
-		ssh_encode_identity_rsa1(&msg, key->rsa, comment);
+		if ((r = sshbuf_put_u8(msg, type)) != 0 ||
+		    (r = ssh_encode_identity_rsa1(msg, key->rsa, comment)) != 0)
+			goto out;
 		break;
 	case KEY_RSA:
 	case KEY_RSA_CERT:
@@ -563,79 +607,86 @@ ssh_add_identity_constrained(AuthenticationConnection *auth, struct sshkey *key,
 		type = constrained ?
 		    SSH2_AGENTC_ADD_ID_CONSTRAINED :
 		    SSH2_AGENTC_ADD_IDENTITY;
-		buffer_put_char(&msg, type);
-		ssh_encode_identity_ssh2(&msg, key, comment);
-		break;
+		if ((r = sshbuf_put_u8(msg, type)) != 0 ||
+		    (r = ssh_encode_identity_ssh2(msg, key, comment)) != 0)
+			goto out;
 	default:
-		buffer_free(&msg);
-		return 0;
+		r = SSH_ERR_INVALID_ARGUMENT;
+		goto out;
 	}
-	if (constrained) {
-		if (life != 0) {
-			buffer_put_char(&msg, SSH_AGENT_CONSTRAIN_LIFETIME);
-			buffer_put_int(&msg, life);
-		}
-		if (confirm != 0)
-			buffer_put_char(&msg, SSH_AGENT_CONSTRAIN_CONFIRM);
-	}
-	if (ssh_request_reply(auth, &msg, &msg) == 0) {
-		buffer_free(&msg);
-		return 0;
-	}
-	type = buffer_get_char(&msg);
-	buffer_free(&msg);
-	return decode_reply(type);
+	if (constrained &&
+	    (r = encode_constraints(msg, life, confirm)) != 0)
+		goto out;
+	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
+		goto out;
+	if ((r = sshbuf_get_u8(msg, &type)) != 0)
+		goto out;
+	r = decode_reply(type);
+ out:
+	sshbuf_free(msg);
+	return r;
 }
 
 /*
- * Removes an identity from the authentication server.  This call is not
- * meant to be used by normal applications.
+ * Removes an identity from the authentication server.
+ * This call is intended only for use by ssh-add(1) and like applications.
  */
-
 int
-ssh_remove_identity(AuthenticationConnection *auth, struct sshkey *key)
+ssh_remove_identity(int sock, struct sshkey *key)
 {
-	Buffer msg;
-	int r, type;
-	u_char *blob;
+	struct sshbuf *msg;
+	int r;
+	u_char type, *blob = NULL;
 	u_int blen;
 
-	buffer_init(&msg);
+	if ((msg = sshbuf_new()) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
 
 	if (key->type == KEY_RSA1) {
-		buffer_put_char(&msg, SSH_AGENTC_REMOVE_RSA_IDENTITY);
-		buffer_put_int(&msg, BN_num_bits(key->rsa->n));
-		buffer_put_bignum(&msg, key->rsa->e);
-		buffer_put_bignum(&msg, key->rsa->n);
+		if ((r = sshbuf_put_u8(msg,
+		    SSH_AGENTC_REMOVE_RSA_IDENTITY)) != 0 ||
+		    (r = sshbuf_put_u32(msg, BN_num_bits(key->rsa->n))) != 0 ||
+		    (r = sshbuf_put_bignum1(msg, key->rsa->e)) != 0 ||
+		    (r = sshbuf_put_bignum1(msg, key->rsa->n)) != 0)
+			goto out;
 	} else if (sshkey_type_plain(key->type) == KEY_DSA ||
 	    sshkey_type_plain(key->type) == KEY_RSA ||
 	    sshkey_type_plain(key->type) == KEY_ECDSA) {
-		if ((r = sshkey_to_blob(key, &blob, &blen)) != 0) {
-			error("%s: sshkey_to_blob: %s", __func__, ssh_err(r));
-			return 0;
-		}
-		buffer_put_char(&msg, SSH2_AGENTC_REMOVE_IDENTITY);
-		buffer_put_string(&msg, blob, blen);
-		xfree(blob);
+		if ((r = sshkey_to_blob(key, &blob, &blen)) != 0)
+			goto out;
+		if ((r = sshbuf_put_u8(msg,
+		    SSH2_AGENTC_REMOVE_IDENTITY)) != 0 ||
+		    (r = sshbuf_put_string(msg, blob, blen)) != 0)
+			goto out;
 	} else {
-		buffer_free(&msg);
-		return 0;
+		r = SSH_ERR_INVALID_ARGUMENT;
+		goto out;
 	}
-	if (ssh_request_reply(auth, &msg, &msg) == 0) {
-		buffer_free(&msg);
-		return 0;
+	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
+		goto out;
+	if ((r = sshbuf_get_u8(msg, &type)) != 0)
+		goto out;
+	r = decode_reply(type);
+ out:
+	if (blob != NULL) {
+		bzero(blob, blen);
+		free(blob);
 	}
-	type = buffer_get_char(&msg);
-	buffer_free(&msg);
-	return decode_reply(type);
+	sshbuf_free(msg);
+	return r;
 }
 
+/*
+ * Add/remove an token-based identity from the authentication server.
+ * This call is intended only for use by ssh-add(1) and like applications.
+ */
 int
-ssh_update_card(AuthenticationConnection *auth, int add,
-    const char *reader_id, const char *pin, u_int life, u_int confirm)
+ssh_update_card(int sock, int add, const char *reader_id, const char *pin,
+    u_int life, u_int confirm)
 {
-	Buffer msg;
-	int type, constrained = (life || confirm);
+	struct sshbuf *msg;
+	int r, constrained = (life || confirm);
+	u_char type;
 
 	if (add) {
 		type = constrained ?
@@ -644,69 +695,48 @@ ssh_update_card(AuthenticationConnection *auth, int add,
 	} else
 		type = SSH_AGENTC_REMOVE_SMARTCARD_KEY;
 
-	buffer_init(&msg);
-	buffer_put_char(&msg, type);
-	buffer_put_cstring(&msg, reader_id);
-	buffer_put_cstring(&msg, pin);
-
-	if (constrained) {
-		if (life != 0) {
-			buffer_put_char(&msg, SSH_AGENT_CONSTRAIN_LIFETIME);
-			buffer_put_int(&msg, life);
-		}
-		if (confirm != 0)
-			buffer_put_char(&msg, SSH_AGENT_CONSTRAIN_CONFIRM);
-	}
-
-	if (ssh_request_reply(auth, &msg, &msg) == 0) {
-		buffer_free(&msg);
-		return 0;
-	}
-	type = buffer_get_char(&msg);
-	buffer_free(&msg);
-	return decode_reply(type);
+	if ((msg = sshbuf_new()) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+	if ((r = sshbuf_put_u8(msg, type)) != 0 ||
+	    (r = sshbuf_put_cstring(msg, reader_id)) != 0 ||
+	    (r = sshbuf_put_cstring(msg, pin)) != 0)
+		goto out;
+	if (constrained &&
+	    (r = encode_constraints(msg, life, confirm)) != 0)
+		goto out;
+	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
+		goto out;
+	if ((r = sshbuf_get_u8(msg, &type)) != 0)
+		goto out;
+	r = decode_reply(type);
+ out:
+	sshbuf_free(msg);
+	return r;
 }
 
 /*
- * Removes all identities from the agent.  This call is not meant to be used
- * by normal applications.
+ * Removes all identities from the agent.
+ * This call is intended only for use by ssh-add(1) and like applications.
  */
-
 int
-ssh_remove_all_identities(AuthenticationConnection *auth, int version)
+ssh_remove_all_identities(int sock, int version)
 {
-	Buffer msg;
-	int type;
-	int code = (version==1) ?
-		SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES :
-		SSH2_AGENTC_REMOVE_ALL_IDENTITIES;
+	struct sshbuf *msg;
+	u_char type = (version == 1) ?
+	    SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES :
+	    SSH2_AGENTC_REMOVE_ALL_IDENTITIES;
+	int r;
 
-	buffer_init(&msg);
-	buffer_put_char(&msg, code);
-
-	if (ssh_request_reply(auth, &msg, &msg) == 0) {
-		buffer_free(&msg);
-		return 0;
-	}
-	type = buffer_get_char(&msg);
-	buffer_free(&msg);
-	return decode_reply(type);
-}
-
-int
-decode_reply(int type)
-{
-	switch (type) {
-	case SSH_AGENT_FAILURE:
-	case SSH_COM_AGENT2_FAILURE:
-	case SSH2_AGENT_FAILURE:
-		logit("SSH_AGENT_FAILURE");
-		return 0;
-	case SSH_AGENT_SUCCESS:
-		return 1;
-	default:
-		fatal("Bad response from authentication agent: %d", type);
-	}
-	/* NOTREACHED */
-	return 0;
+	if ((msg = sshbuf_new()) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+	if ((r = sshbuf_put_u8(msg, type)) != 0)
+		goto out;
+	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
+		goto out;
+	if ((r = sshbuf_get_u8(msg, &type)) != 0)
+		goto out;
+	r = decode_reply(type);
+ out:
+	sshbuf_free(msg);
+	return r;
 }
diff --git a/ssh/authfd.h b/ssh/authfd.h
index 3f0d784..09cdf02 100644
--- a/ssh/authfd.h
+++ b/ssh/authfd.h
@@ -16,6 +16,33 @@
 #ifndef AUTHFD_H
 #define AUTHFD_H
 
+/* List of identities returned by ssh_fetch_identitylist() */
+struct ssh_identitylist {
+	size_t nkeys;
+	struct sshkey **keys;
+	char **comments;
+};
+
+int	ssh_get_authentication_socket(int *fdp);
+void	ssh_close_authentication_socket(int sock);
+
+int	ssh_lock_agent(int sock, int lock, const char *password);
+int	ssh_fetch_identitylist(int sock, int version,
+	    struct ssh_identitylist **idlp);
+void	ssh_free_identitylist(struct ssh_identitylist *idl);
+int	ssh_add_identity_constrained(int sock, struct sshkey *key,
+	    const char *comment, u_int life, u_int confirm);
+int	ssh_remove_identity(int sock, struct sshkey *key);
+int	ssh_update_card(int sock, int add, const char *reader_id,
+	    const char *pin, u_int life, u_int confirm);
+int	ssh_remove_all_identities(int sock, int version);
+
+int	ssh_decrypt_challenge(int sock, struct sshkey* key, BIGNUM *challenge,
+	    u_char session_id[16], u_char response[16]);
+int	ssh_agent_sign(int sock, struct sshkey *key,
+	    u_char **sigp, u_int *lenp,
+	    u_char *data, u_int datalen, u_int compat);
+
 /* Messages for the authentication agent connection. */
 #define SSH_AGENTC_REQUEST_RSA_IDENTITIES	1
 #define SSH_AGENT_RSA_IDENTITIES_ANSWER		2
@@ -60,34 +87,4 @@
 
 #define	SSH_AGENT_OLD_SIGNATURE			0x01
 
-typedef struct {
-	int	fd;
-	Buffer	identities;
-	int	howmany;
-}	AuthenticationConnection;
-
-int	ssh_agent_present(void);
-int	ssh_get_authentication_socket(void);
-void	ssh_close_authentication_socket(int);
-
-AuthenticationConnection *ssh_get_authentication_connection(void);
-void	ssh_close_authentication_connection(AuthenticationConnection *);
-int	 ssh_get_num_identities(AuthenticationConnection *, int);
-struct sshkey *ssh_get_first_identity(AuthenticationConnection *, char **, int);
-struct sshkey *ssh_get_next_identity(AuthenticationConnection *, char **, int);
-int	 ssh_add_identity_constrained(AuthenticationConnection *,
-    struct sshkey *, const char *, u_int, u_int);
-int	 ssh_remove_identity(AuthenticationConnection *, struct sshkey *);
-int	 ssh_remove_all_identities(AuthenticationConnection *, int);
-int	 ssh_lock_agent(AuthenticationConnection *, int, const char *);
-int	 ssh_update_card(AuthenticationConnection *, int, const char *,
-    const char *, u_int, u_int);
-
-int	 ssh_decrypt_challenge(AuthenticationConnection *, struct sshkey *,
-    BIGNUM *, u_char[16], u_int, u_char[16]);
-
-int
-ssh_agent_sign(AuthenticationConnection *, struct sshkey *,
-    u_char **, u_int *, u_char *, u_int, u_int);
-
 #endif				/* AUTHFD_H */
diff --git a/ssh/clientloop.c b/ssh/clientloop.c
index 4c64225..579d30d 100644
--- a/ssh/clientloop.c
+++ b/ssh/clientloop.c
@@ -1705,7 +1705,7 @@ static int
 client_input_agent_open(int type, u_int32_t seq, struct ssh *ssh)
 {
 	Channel *c = NULL;
-	int remote_id, sock;
+	int remote_id, sock, r;
 
 	/* Read the remote channel number from the message. */
 	remote_id = ssh_packet_get_int(ssh);
@@ -1715,7 +1715,10 @@ client_input_agent_open(int type, u_int32_t seq, struct ssh *ssh)
 	 * Get a connection to the local authentication agent (this may again
 	 * get forwarded).
 	 */
-	sock = ssh_get_authentication_socket();
+	if ((r = ssh_get_authentication_socket(&sock)) != 0 &&
+	    r != SSH_ERR_AGENT_NOT_PRESENT)
+		debug("%s: ssh_get_authentication_socket: %s",
+		    __func__, ssh_err(r));
 
 	/*
 	 * If we could not connect the agent, send an error message back to
@@ -1723,7 +1726,7 @@ client_input_agent_open(int type, u_int32_t seq, struct ssh *ssh)
 	 * because authentication forwarding is only enabled if we have an
 	 * agent.
 	 */
-	if (sock >= 0) {
+	if (r == 0) {
 		c = channel_new("", SSH_CHANNEL_OPEN, sock, sock,
 		    -1, 0, 0, 0, "authentication agent connection", 1);
 		c->remote_id = remote_id;
@@ -1814,7 +1817,7 @@ static Channel *
 client_request_agent(struct ssh *ssh, const char *request_type, int rchan)
 {
 	Channel *c = NULL;
-	int sock;
+	int r, sock;
 
 	if (!options.forward_agent) {
 		error("Warning: ssh server tried agent forwarding.");
@@ -1822,9 +1825,12 @@ client_request_agent(struct ssh *ssh, const char *request_type, int rchan)
 		    "malicious server.");
 		return NULL;
 	}
-	sock = ssh_get_authentication_socket();
-	if (sock < 0)
+	if ((r = ssh_get_authentication_socket(&sock)) != 0) {
+		if (r != SSH_ERR_AGENT_NOT_PRESENT)
+			debug("%s: ssh_get_authentication_socket: %s",
+			    __func__, ssh_err(r));
 		return NULL;
+	}
 	c = channel_new("authentication agent connection",
 	    SSH_CHANNEL_OPEN, sock, sock, -1,
 	    CHAN_X11_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0,
diff --git a/ssh/err.c b/ssh/err.c
index 2398012..9093a6e 100644
--- a/ssh/err.c
+++ b/ssh/err.c
@@ -115,6 +115,10 @@ ssh_err(int n)
 		return "certificate does not match key";
 	case SSH_ERR_KEY_NOT_FOUND:
 		return "key not found";
+	case SSH_ERR_AGENT_NOT_PRESENT:
+		return "agent not present";
+	case SSH_ERR_AGENT_NO_IDENTITIES:
+		return "agent contains no identities";
 	default:
 		return "unknown error";
 	}
diff --git a/ssh/err.h b/ssh/err.h
index 52f89f1..7eea8e9 100644
--- a/ssh/err.h
+++ b/ssh/err.h
@@ -67,6 +67,8 @@
 #define SSH_ERR_KEY_BAD_PERMISSIONS		-43
 #define SSH_ERR_KEY_CERT_MISMATCH		-44
 #define SSH_ERR_KEY_NOT_FOUND			-45
+#define SSH_ERR_AGENT_NOT_PRESENT		-46
+#define SSH_ERR_AGENT_NO_IDENTITIES		-47
 
 
 /* Translate a numeric error code to a human-readable error string */
diff --git a/ssh/ssh-add.c b/ssh/ssh-add.c
index 63accb0..fb9c1a5 100644
--- a/ssh/ssh-add.c
+++ b/ssh/ssh-add.c
@@ -91,7 +91,7 @@ clear_pass(void)
 }
 
 static int
-delete_file(AuthenticationConnection *ac, const char *filename)
+delete_file(int agent_fd, const char *filename)
 {
 	struct sshkey *public;
 	char *comment = NULL;
@@ -101,11 +101,12 @@ delete_file(AuthenticationConnection *ac, const char *filename)
 		printf("Bad key file %s: %s\n", filename, ssh_err(r));
 		return -1;
 	}
-	if (ssh_remove_identity(ac, public)) {
+	if ((r = ssh_remove_identity(agent_fd, public)) == 0) {
 		fprintf(stderr, "Identity removed: %s (%s)\n", filename, comment);
 		ret = 0;
 	} else
-		fprintf(stderr, "Could not remove identity: %s\n", filename);
+		fprintf(stderr, "Could not remove identity \"%s\": %s\n",
+		    filename, ssh_err(r));
 
 	sshkey_free(public);
 	xfree(comment);
@@ -115,14 +116,15 @@ delete_file(AuthenticationConnection *ac, const char *filename)
 
 /* Send a request to remove all identities. */
 static int
-delete_all(AuthenticationConnection *ac)
+delete_all(int agent_fd)
 {
 	int ret = -1;
 
-	if (ssh_remove_all_identities(ac, 1))
+	if (ssh_remove_all_identities(agent_fd, 1) == 0)
 		ret = 0;
 	/* ignore error-code for ssh2 */
-	ssh_remove_all_identities(ac, 2);
+	/* XXX revisit */
+	ssh_remove_all_identities(agent_fd, 2);
 
 	if (ret == 0)
 		fprintf(stderr, "All identities removed.\n");
@@ -133,7 +135,7 @@ delete_all(AuthenticationConnection *ac)
 }
 
 static int
-add_file(AuthenticationConnection *ac, const char *filename, int key_only)
+add_file(int agent_fd, const char *filename, int key_only)
 {
 	struct sshkey *private, *cert;
 	char *comment = NULL;
@@ -219,8 +221,8 @@ add_file(AuthenticationConnection *ac, const char *filename, int key_only)
 	}
 	buffer_free(&keyblob);
 
-	if (ssh_add_identity_constrained(ac, private, comment, lifetime,
-	    confirm)) {
+	if ((r = ssh_add_identity_constrained(agent_fd, private, comment,
+	    lifetime, confirm)) == 0) {
 		fprintf(stderr, "Identity added: %s (%s)\n", filename, comment);
 		ret = 0;
 		if (lifetime != 0)
@@ -230,7 +232,8 @@ add_file(AuthenticationConnection *ac, const char *filename, int key_only)
 			fprintf(stderr,
 			    "The user must confirm each use of the key\n");
 	} else {
-		fprintf(stderr, "Could not add identity: %s\n", filename);
+		fprintf(stderr, "Could not add identity \"%s\": %s\n",
+		    filename, ssh_err(r));
 	}
 
 	/* Skip trying to load the cert if requested */
@@ -266,10 +269,11 @@ add_file(AuthenticationConnection *ac, const char *filename, int key_only)
 	}
 	sshkey_free(cert);
 
-	if (!ssh_add_identity_constrained(ac, private, comment,
-	    lifetime, confirm)) {
-		error("Certificate %s (%s) add failed", certpath,
-		    private->cert->key_id);
+	if ((r = ssh_add_identity_constrained(agent_fd, private, comment,
+	    lifetime, confirm)) != 0) {
+		error("Certificate %s (%s) add failed: %s", certpath,
+		    private->cert->key_id, ssh_err(r));
+		goto out;
 	}
 	fprintf(stderr, "Certificate added: %s (%s)\n", certpath,
 	    private->cert->key_id);
@@ -287,22 +291,23 @@ add_file(AuthenticationConnection *ac, const char *filename, int key_only)
 }
 
 static int
-update_card(AuthenticationConnection *ac, int add, const char *id)
+update_card(int agent_fd, int add, const char *id)
 {
 	char *pin;
-	int ret = -1;
+	int r, ret = -1;
 
 	pin = read_passphrase("Enter passphrase for PKCS#11: ", RP_ALLOW_STDIN);
 	if (pin == NULL)
 		return -1;
 
-	if (ssh_update_card(ac, add, id, pin, lifetime, confirm)) {
+	if ((r = ssh_update_card(agent_fd, add, id, pin, lifetime,
+	    confirm)) == 0) {
 		fprintf(stderr, "Card %s: %s\n",
 		    add ? "added" : "removed", id);
 		ret = 0;
 	} else {
-		fprintf(stderr, "Could not %s card: %s\n",
-		    add ? "add" : "remove", id);
+		fprintf(stderr, "Could not %s card \"%s\": %s\n",
+		    add ? "add" : "remove", id, ssh_err(r));
 		ret = -1;
 	}
 	xfree(pin);
@@ -310,33 +315,42 @@ update_card(AuthenticationConnection *ac, int add, const char *id)
 }
 
 static int
-list_identities(AuthenticationConnection *ac, int do_fp)
+list_identities(int agent_fd, int do_fp)
 {
-	struct sshkey *key;
-	char *comment, *fp;
+	char *fp;
 	int version, r, had_identities = 0;
+	struct ssh_identitylist *idlist;
+	size_t i;
 
 	for (version = 1; version <= 2; version++) {
-		for (key = ssh_get_first_identity(ac, &comment, version);
-		    key != NULL;
-		    key = ssh_get_next_identity(ac, &comment, version)) {
+		if ((r = ssh_fetch_identitylist(agent_fd, version,
+		    &idlist)) != 0) {
+			if (r != SSH_ERR_AGENT_NO_IDENTITIES)
+				fprintf(stderr, "error fetching identities for "
+				    "protocol %d: %s\n", version, ssh_err(r));
+			continue;
+		}
+		for (i = 0; i < idlist->nkeys; i++) {
 			had_identities = 1;
 			if (do_fp) {
-				fp = sshkey_fingerprint(key, SSH_FP_MD5,
-				    SSH_FP_HEX);
+				fp = sshkey_fingerprint(idlist->keys[i],
+				    SSH_FP_MD5, SSH_FP_HEX);
 				printf("%d %s %s (%s)\n",
-				    sshkey_size(key), fp, comment,
-				    sshkey_type(key));
+				    sshkey_size(idlist->keys[i]), fp,
+				    idlist->comments[i],
+				    sshkey_type(idlist->keys[i]));
 				xfree(fp);
 			} else {
-				if ((r = sshkey_write(key, stdout)) != 0)
-					fprintf(stderr, "sshkey_write: %s",
+				if ((r = sshkey_write(idlist->keys[i],
+				    stdout)) != 0) {
+					fprintf(stderr, "sshkey_write: %s\n",
 					    ssh_err(r));
-				fprintf(stdout, " %s\n", comment);
+					continue;
+				}
+				fprintf(stdout, " %s\n", idlist->comments[i]);
 			}
-			sshkey_free(key);
-			xfree(comment);
 		}
+		ssh_free_identitylist(idlist);
 	}
 	if (!had_identities) {
 		printf("The agent has no identities.\n");
@@ -346,10 +360,10 @@ list_identities(AuthenticationConnection *ac, int do_fp)
 }
 
 static int
-lock_agent(AuthenticationConnection *ac, int lock)
+lock_agent(int agent_fd, int lock)
 {
 	char prompt[100], *p1, *p2;
-	int passok = 1, ret = -1;
+	int r, passok = 1, ret = -1;
 
 	strlcpy(prompt, "Enter lock password: ", sizeof(prompt));
 	p1 = read_passphrase(prompt, RP_ALLOW_STDIN);
@@ -363,24 +377,28 @@ lock_agent(AuthenticationConnection *ac, int lock)
 		memset(p2, 0, strlen(p2));
 		xfree(p2);
 	}
-	if (passok && ssh_lock_agent(ac, lock, p1)) {
-		fprintf(stderr, "Agent %slocked.\n", lock ? "" : "un");
-		ret = 0;
-	} else
-		fprintf(stderr, "Failed to %slock agent.\n", lock ? "" : "un");
+	if (passok) {
+		if ((r = ssh_lock_agent(agent_fd, lock, p1)) == 0) {
+			fprintf(stderr, "Agent %slocked.\n", lock ? "" : "un");
+			ret = 0;
+		} else {
+			fprintf(stderr, "Failed to %slock agent: %sn",
+			    lock ? "" : "un", ssh_err(r));
+		}
+	}
 	memset(p1, 0, strlen(p1));
 	xfree(p1);
 	return (ret);
 }
 
 static int
-do_file(AuthenticationConnection *ac, int deleting, int key_only, char *file)
+do_file(int agent_fd, int deleting, int key_only, char *file)
 {
 	if (deleting) {
-		if (delete_file(ac, file) == -1)
+		if (delete_file(agent_fd, file) == -1)
 			return -1;
 	} else {
-		if (add_file(ac, file, key_only) == -1)
+		if (add_file(agent_fd, file, key_only) == -1)
 			return -1;
 	}
 	return 0;
@@ -409,22 +427,28 @@ main(int argc, char **argv)
 {
 	extern char *optarg;
 	extern int optind;
-	AuthenticationConnection *ac = NULL;
+	int agent_fd;
 	char *pkcs11provider = NULL;
-	int i, ch, deleting = 0, ret = 0, key_only = 0;
+	int r, i, ch, deleting = 0, ret = 0, key_only = 0;
 
 	/* Ensure that fds 0, 1 and 2 are open or directed to /dev/null */
 	sanitise_stdfd();
 
 	OpenSSL_add_all_algorithms();
 
-	/* At first, get a connection to the authentication agent. */
-	ac = ssh_get_authentication_connection();
-	if (ac == NULL) {
-		fprintf(stderr,
-		    "Could not open a connection to your authentication agent.\n");
+	/* First, get a connection to the authentication agent. */
+	switch (r = ssh_get_authentication_socket(&agent_fd)) {
+	case 0:
+		break;
+	case SSH_ERR_AGENT_NOT_PRESENT:
+		fprintf(stderr, "Could not open a connection to your "
+		    "authentication agent.\n");
+		exit(2);
+	default:
+		fprintf(stderr, "Error connecting to agent: %s\n", ssh_err(r));
 		exit(2);
 	}
+
 	while ((ch = getopt(argc, argv, "klLcdDxXe:s:t:")) != -1) {
 		switch (ch) {
 		case 'k':
@@ -432,12 +456,12 @@ main(int argc, char **argv)
 			break;
 		case 'l':
 		case 'L':
-			if (list_identities(ac, ch == 'l' ? 1 : 0) == -1)
+			if (list_identities(agent_fd, ch == 'l' ? 1 : 0) == -1)
 				ret = 1;
 			goto done;
 		case 'x':
 		case 'X':
-			if (lock_agent(ac, ch == 'x' ? 1 : 0) == -1)
+			if (lock_agent(agent_fd, ch == 'x' ? 1 : 0) == -1)
 				ret = 1;
 			goto done;
 		case 'c':
@@ -447,7 +471,7 @@ main(int argc, char **argv)
 			deleting = 1;
 			break;
 		case 'D':
-			if (delete_all(ac) == -1)
+			if (delete_all(agent_fd) == -1)
 				ret = 1;
 			goto done;
 		case 's':
@@ -473,7 +497,7 @@ main(int argc, char **argv)
 	argc -= optind;
 	argv += optind;
 	if (pkcs11provider != NULL) {
-		if (update_card(ac, !deleting, pkcs11provider) == -1)
+		if (update_card(agent_fd, !deleting, pkcs11provider) == -1)
 			ret = 1;
 		goto done;
 	}
@@ -495,7 +519,7 @@ main(int argc, char **argv)
 			    default_files[i]);
 			if (stat(buf, &st) < 0)
 				continue;
-			if (do_file(ac, deleting, key_only, buf) == -1)
+			if (do_file(agent_fd, deleting, key_only, buf) == -1)
 				ret = 1;
 			else
 				count++;
@@ -504,13 +528,14 @@ main(int argc, char **argv)
 			ret = 1;
 	} else {
 		for (i = 0; i < argc; i++) {
-			if (do_file(ac, deleting, key_only, argv[i]) == -1)
+			if (do_file(agent_fd, deleting, key_only,
+			    argv[i]) == -1)
 				ret = 1;
 		}
 	}
 	clear_pass();
 
 done:
-	ssh_close_authentication_connection(ac);
+	ssh_close_authentication_socket(agent_fd);
 	return ret;
 }
diff --git a/ssh/ssh.c b/ssh/ssh.c
index 0b22a64..90656ec 100644
--- a/ssh/ssh.c
+++ b/ssh/ssh.c
@@ -1129,10 +1129,16 @@ ssh_init_forwarding(struct ssh *ssh)
 static void
 check_agent_present(void)
 {
+	int r;
+
 	if (options.forward_agent) {
 		/* Clear agent forwarding if we don't have an agent. */
-		if (!ssh_agent_present())
+		if ((r = ssh_get_authentication_socket(NULL)) != 0) {
 			options.forward_agent = 0;
+			if (r != SSH_ERR_AGENT_NOT_PRESENT)
+				debug("ssh_get_authentication_socket: %s",
+				    ssh_err(r));
+		}
 	}
 }
 
diff --git a/ssh/sshconnect1.c b/ssh/sshconnect1.c
index 89c0c78..e487d93 100644
--- a/ssh/sshconnect1.c
+++ b/ssh/sshconnect1.c
@@ -61,33 +61,41 @@ extern char *__progname;
 static int
 try_agent_authentication(void)
 {
-	int type;
-	char *comment;
-	AuthenticationConnection *auth;
+	int r, type, agent_fd, ret = 0;
 	u_char response[16];
-	u_int i;
-	struct sshkey *key;
+	size_t i;
 	BIGNUM *challenge;
+	struct ssh_identitylist *idlist = NULL;
 
 	/* Get connection to the agent. */
-	auth = ssh_get_authentication_connection();
-	if (!auth)
+	if ((r = ssh_get_authentication_socket(&agent_fd)) != 0) {
+		if (r != SSH_ERR_AGENT_NOT_PRESENT)
+			debug("%s: ssh_get_authentication_socket: %s",
+			    __func__, ssh_err(r));
 		return 0;
+	}
 
 	if ((challenge = BN_new()) == NULL)
 		fatal("try_agent_authentication: BN_new failed");
+
 	/* Loop through identities served by the agent. */
-	for (key = ssh_get_first_identity(auth, &comment, 1);
-	    key != NULL;
-	    key = ssh_get_next_identity(auth, &comment, 1)) {
-
+	if ((r = ssh_fetch_identitylist(agent_fd, 1, &idlist)) != 0) {
+		if (r != SSH_ERR_AGENT_NO_IDENTITIES)
+			debug("%s: ssh_fetch_identitylist: %s",
+			    __func__, ssh_err(r));
+		goto out;
+	}
+	for (i = 0; i < idlist->nkeys; i++) {
 		/* Try this identity. */
-		debug("Trying RSA authentication via agent with '%.100s'", comment);
-		xfree(comment);
+		debug("Trying RSA authentication via agent with '%.100s'",
+		    idlist->comments[i]);
 
-		/* Tell the server that we are willing to authenticate using this key. */
+		/*
+		 * Tell the server that we are willing to authenticate
+		 * using this key.
+		 */
 		packet_start(SSH_CMSG_AUTH_RSA);
-		packet_put_bignum(key->rsa->n);
+		packet_put_bignum(idlist->keys[i]->rsa->n);
 		packet_send();
 		packet_write_wait();
 
@@ -98,7 +106,6 @@ try_agent_authentication(void)
 		   does not support RSA authentication. */
 		if (type == SSH_SMSG_FAILURE) {
 			debug("Server refused our key.");
-			sshkey_free(key);
 			continue;
 		}
 		/* Otherwise it should have sent a challenge. */
@@ -112,16 +119,17 @@ try_agent_authentication(void)
 		debug("Received RSA challenge from server.");
 
 		/* Ask the agent to decrypt the challenge. */
-		if (!ssh_decrypt_challenge(auth, key, challenge, session_id, 1, response)) {
+		if ((r = ssh_decrypt_challenge(agent_fd, idlist->keys[i],
+		    challenge, session_id, response)) != 0) {
 			/*
 			 * The agent failed to authenticate this identifier
 			 * although it advertised it supports this.  Just
 			 * return a wrong value.
 			 */
-			logit("Authentication agent failed to decrypt challenge.");
+			logit("Authentication agent failed to decrypt i"
+			    "challenge.");
 			memset(response, 0, sizeof(response));
 		}
-		sshkey_free(key);
 		debug("Sending response to RSA challenge.");
 
 		/* Send the decrypted challenge back to the server. */
@@ -134,22 +142,26 @@ try_agent_authentication(void)
 		/* Wait for response from the server. */
 		type = packet_read();
 
-		/* The server returns success if it accepted the authentication. */
+		/*
+		 * The server returns success if it accepted the
+		 * authentication.
+		 */
 		if (type == SSH_SMSG_SUCCESS) {
-			ssh_close_authentication_connection(auth);
-			BN_clear_free(challenge);
 			debug("RSA authentication accepted by server.");
-			return 1;
+			ret = 1;
+			goto out;
 		}
 		/* Otherwise it should return failure. */
 		if (type != SSH_SMSG_FAILURE)
-			packet_disconnect("Protocol error waiting RSA auth response: %d",
-					  type);
+			packet_disconnect("Protocol error waiting RSA auth "
+			    "response: %d", type);
 	}
-	ssh_close_authentication_connection(auth);
-	BN_clear_free(challenge);
 	debug("RSA authentication using agent refused.");
-	return 0;
+ out:
+	ssh_free_identitylist(idlist);
+	ssh_close_authentication_socket(agent_fd);
+	BN_clear_free(challenge);
+	return ret;
 }
 
 /*
diff --git a/ssh/sshconnect2.c b/ssh/sshconnect2.c
index 77cd317..e06c6ec 100644
--- a/ssh/sshconnect2.c
+++ b/ssh/sshconnect2.c
@@ -236,7 +236,7 @@ typedef struct idlist Idlist;
 
 struct identity {
 	TAILQ_ENTRY(identity) next;
-	AuthenticationConnection *ac;	/* set if agent supports key */
+	int	agent_fd;		/* >=0 if agent supports key */
 	struct sshkey	*key;		/* public/private key */
 	char	*filename;		/* comment for agent-only keys */
 	int	tried;
@@ -255,7 +255,7 @@ struct Authctxt {
 	int attempt;
 	/* pubkey */
 	Idlist keys;
-	AuthenticationConnection *agent;
+	int agent_fd;
 	/* hostbased */
 	Sensitive *sensitive;
 	/* kbd-interactive */
@@ -1200,9 +1200,9 @@ identity_sign(Identity *id, u_char **sigp, u_int *lenp,
 	int ret;
 
 	/* the agent supports this key */
-	if (id->ac)
-		return (ssh_agent_sign(id->ac, id->key, sigp, lenp,
-		    data, datalen, compat));
+	if (id->agent_fd)
+		return ssh_agent_sign(id->agent_fd, id->key, sigp, lenp,
+		    data, datalen, compat);
 	/*
 	 * we have already loaded the private key or
 	 * the private key is stored in external hardware
@@ -1414,9 +1414,9 @@ pubkey_prepare(struct ssh *ssh)
 	Identity *id;
 	Idlist agent, files, *preferred;
 	struct sshkey *key;
-	AuthenticationConnection *ac;
-	char *comment;
-	int i, found;
+	int agent_fd, i, r, found;
+	size_t j;
+	struct ssh_identitylist *idlist;
 
 	TAILQ_INIT(&agent);	/* keys from the agent */
 	TAILQ_INIT(&files);	/* keys from the config file */
@@ -1437,37 +1437,48 @@ pubkey_prepare(struct ssh *ssh)
 		TAILQ_INSERT_TAIL(&files, id, next);
 	}
 	/* list of keys supported by the agent */
-	if ((ac = ssh_get_authentication_connection())) {
-		for (key = ssh_get_first_identity(ac, &comment, 2);
-		    key != NULL;
-		    key = ssh_get_next_identity(ac, &comment, 2)) {
+	if ((r = ssh_get_authentication_socket(&agent_fd)) != 0) {
+		if (r != SSH_ERR_AGENT_NOT_PRESENT)
+			debug("%s: ssh_get_authentication_socket: %s",
+			    __func__, ssh_err(r));
+	} else if ((r = ssh_fetch_identitylist(agent_fd, 2, &idlist)) != 0) {
+		if (r != SSH_ERR_AGENT_NO_IDENTITIES)
+			debug("%s: ssh_fetch_identitylist: %s",
+			    __func__, ssh_err(r));
+	} else {
+		for (j = 0; j < idlist->nkeys; j++) {
 			found = 0;
 			TAILQ_FOREACH(id, &files, next) {
-				/* agent keys from the config file are preferred */
-				if (sshkey_equal(key, id->key)) {
-					sshkey_free(key);
-					xfree(comment);
+				/*
+				 * agent keys from the config file are
+				 * preferred
+				 */
+				if (sshkey_equal(idlist->keys[j], id->key)) {
 					TAILQ_REMOVE(&files, id, next);
 					TAILQ_INSERT_TAIL(preferred, id, next);
-					id->ac = ac;
+					id->agent_fd = agent_fd;
 					found = 1;
 					break;
 				}
 			}
 			if (!found && !options.identities_only) {
 				id = xcalloc(1, sizeof(*id));
-				id->key = key;
-				id->filename = comment;
-				id->ac = ac;
+				/* XXX "steals" key/comment from idlist */
+				id->key = idlist->keys[j];
+				id->filename = idlist->comments[j];
+				idlist->keys[j] = NULL;
+				idlist->comments[j] = NULL;
+				id->agent_fd = agent_fd;
 				TAILQ_INSERT_TAIL(&agent, id, next);
 			}
 		}
+		ssh_free_identitylist(idlist);
 		/* append remaining agent keys */
 		for (id = TAILQ_FIRST(&agent); id; id = TAILQ_FIRST(&agent)) {
 			TAILQ_REMOVE(&agent, id, next);
 			TAILQ_INSERT_TAIL(preferred, id, next);
 		}
-		authctxt->agent = ac;
+		authctxt->agent_fd = agent_fd;
 	}
 	/* append remaining keys from the config file */
 	for (id = TAILQ_FIRST(&files); id; id = TAILQ_FIRST(&files)) {
@@ -1485,8 +1496,8 @@ pubkey_cleanup(struct ssh *ssh)
 	Authctxt *authctxt = ssh->authctxt;
 	Identity *id;
 
-	if (authctxt->agent != NULL)
-		ssh_close_authentication_connection(authctxt->agent);
+	if (authctxt->agent_fd != -1)
+		ssh_close_authentication_socket(authctxt->agent_fd);
 	for (id = TAILQ_FIRST(&authctxt->keys); id;
 	    id = TAILQ_FIRST(&authctxt->keys)) {
 		TAILQ_REMOVE(&authctxt->keys, id, next);